Modern genetics began with the experiments of Gregor Mendel. In his careful and quantitative work with garden peas, Mendel discovered that discrete units called genes are responsible for inheritance. Mendel's laws, which reflect the rules of probability, explain the characteristics and proportions of offspring born to a particular set of parents. Modern geneticists continue to extend the principles discovered by Mendel to new organisms and more complex patterns of inheritance.
             Gregor Mendel formulated a particular theory of inheritance based on experiments with garden peas, carried out in the 1860's. Using simple pea pod plants, Mendel studied seven basic characteristics of the pea pod plants. By tracing these characteristics, Mendel discovered three basic laws which governed the passage of a trait from one member of a species to another member of the same species.
             Mendel's First Law - the law of segregation; during gamete formation each member of the allelic pair separates from the other member to form the genetic constitution of the gamete. He arrived at this law by making hybrid offspring and letting them self-pollinate. The F1 generation exhibited the dominant trait, while in the next generation, 75% of the offsprings had the dominant trait and 25% had the recessive trait, for a 3:1 ratio. Mendel's explanation was that genes have alternative forms (alleles) and that each organism inherits one allele for each gene from each parent. These separate (segregate) during gamete formation, so that a sperm or egg carries only one allele. After fertilization if the 2 alleles are different, the dominant allele is expressed in the offspring and the other allele is masked.
             Mendel's Second Law - the law of independent assortment; during gamete formation the segregation of the alleles of one allelic pair is independent of the segregation of the alleles of another allelic pair . Mendel proposed this law based on dihybrid
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